Plasma deposition of thin layers of substrated or the like

ABSTRACT

Device for producing thin layers of mineral substances comprising a vacuum container and a cavity whose walls consist of the substance to be deposited, and having an opening in one of its faces. An electromagnetic field is generated in the cavity to form a plasma.

United States Patent Van Cakenberghe Sept. 23, 1975 PLASMA DEPOSITION OFTHIN LAYERS OF SUBSTRATED OR THE LIKE Inventor: Jean L. Van Cakenberghe,Mons,

Belgium Assignee: Compagnie Industrielle des TelecommunicationsCit-Alcatel, Paris, France Filed: Nov. 21, 1973 Appl. No.: 417,842

Related US. Application Data Division of Ser. No. 246,019, April 20,1972, Pat. No. 3,801,355.

Foreign Application Priority Data Apr. 27, 1971 Belgium 766345 US. Clll8/49.l; l17/93.l PF; 219/10.49;

313/2313 Int. Cl. C23C 13/12 Field of Search 118/491, 49.5;

117/93.1 R, 93.1 GD, 93.1 PF; 219/10.49,

[56] References Cited UNITED STATES PATENTS 3,211,548 10/1965 Schelleret a1. 117/9311 PF X 3,264,508 8/1966 Lai et a1. 21 /121 P X 3,472,67910/1969 Ing, Jr. et a1 1l7/93.l GD X 3,736,175 5/1973 Carleton 118/495 XFOREIGN PATENTS OR APPLICATIONS 1,142,262 l/1963 Germany 1l7/93.1 GD

Primary ExaminerMorris Kaplan Attorney, Agent, or Firm-Sughrue,Rothwell, Mion, Zinn and Macpeak ABSTRACT Device for producing thinlayers of mineral substances comprising a vacuum container and a cavitywhose walls consist of the substance to be deposited, and having anopening in one of its faces. An electromagnetic field is generated inthe cavity to form a plasma.

5 Claims, 3 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of23,906,892

PLASMA DEPOSITION OF THIN LAYERS OF SUBSTRATED OR THE LIKE This is adivision of application Ser. No. 246,019, filed Apr. 20, 1972 now US.Pat. No. 3,801,355.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention concerns a method enabling thin layers of mineral substancesto be deposited, as well as the device for implementing the method.

2. Description of the Prior Art Thin layers are usually produced byevaporation in a vacuum or by a method called reactive projection. Thefirst method can be used only in cases where the substance to bedeposited decomposes when it is brought to a high temperature in avacuum, into elements having very different vapor pressures and the mostvolatile of which can have a vapor pressure which can be measured at thedepositing temperature. Such is the case, more particularly, with themajority of oxides, certain sulphides as well as of gallum arsenide andgallium phosphide.

The second method mentioned above consists in causing the evaporation ofthe material to be deposited in an electrical discharge at low pressure,between two electrodes one of which consists of the material to bedeposited or the metallic component of that material, the othercomponent then being contained in gaseous phase. The material to bedeposited is deposited in the form of a thin layer on a substrate,arranged at a few centimeters from that electrode, which can be incontact or otherwise with the second electrode. In the case where a thinlayer of zinc oxide, for example, is to be deposited, the firstelectrode can consist either of zinc oxide or of metallic zinc with apure gaseous oxygen atmosphere or an atmosphere consisting of oxygenmixed with a neutral gas such as argon.

This second method can certainly be used for the above-mentionedsubstances, but it is unsuitable for semi-conductor materials, for thethin layers thus obtained consist of very small micro-crystals so thatcertain electrical properties such as the mobility and service life ofthe charge carriers are subjected to detrimental influence. Moreover,this second method is characterized by a relatively considerabledissipation of energy and a relatively low depositing speed which can,moreover, vary within wide limits.

The object of the invention is therefore a method for depositing thinlayers which does not have the abovemetnioned disadvantages.

It also provides a device for producing thin layers, either oninsulating supports or on electrically conductive or semi-conductivesupports.

Lastly, it provides a device enabling thin layers of material havingelectrical, semi-conductive, piezoelectrical, magnetic and/or opticalproperties, as well as thin layers of material having a high meltingpoint such as'refractory materials to be produced.

SUMMARY OF THE INVENTION The method enabling thin layers to be depositedin a vacuum on the surface of a substrate arranged adjacent to theopening of a cavity in which a gas is injected at a pre-determinedpressure is characterized in that a plasma is formed inside thecavitypreviously lined on the inside with the substance to be deposited.

The method also enables layers to be deposited on the surface of asubstrate when the cavity consists directly of the substance to bedeposited.

The device implementing the method according to the invention ischaracterized in that it comprises, on the one hand, a high-frequencyexcitation means generating an electromagnetic field, and, on the otherhand, inside a vacuum container, at least a substrate support, asubstrate, a cavity lined on the inside with the substance to bedeposited and having an opening adjacent to the substrate and a meansfor injecting a gas at a predetermined pressure into said cavity,promoting the forming of a plasma within said cavity where there is theelectromagnetic field.

The device implementing the method according to the invention is alsocharacterized in that the support for the substrate comprises anelectrical heating means enabling the substrate to be brought to apredetermined temperature.

In a particular embodiment, the device according to the invention ischaracterized in that it comprises, moreover, an electrode in thecavity, this electrode being connected to an appropriate electricalpotential so as to produce a spark suitable for causing the starting upof the plasma.

The cavity has, to great advantage, a cylindrical shape, the cylindricalwall being provided, on its inside, with longitudinal ribs. Moreover,the insulating container may, to great advantage, be cooled.

The invention will be described herebelow with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS According to FIG. 1, a cylindrical cavity 2, whose wallconsists of, or is lined on the inside with the substance to bedeposited, is arranged inside the tube 1, made of quartz or ceramicmaterial, for example. One

of the transversal faces of the cavity is provided with an opening 3.The high-frequency excitation device consists, here, of an inductionwinding 4 surrounding the tube 1 at the level of the cavity 2. Thiswinding is connected to a high frequency voltage supply 5. A substratesupport 6 is placed so as to have a substrate 7 adjacent to the opening3 in the cavity 2. The electrical heating device 8 enables the substrate7 to be brought to a required temperature. In the embodiment shown byway of an example, the substrate support 6 is arranged so as to be ableto pivot about an axis 9 in order to bring several substratessuccessively before the opening 3.

As shown in FIG. 2, the cylindrical wall of the cavity comprises, on theinside, longitudinal ribs 10 so as to reduce the transmission of heatthrough the wall.

The operation of this device is as follows:

A gas is injected into the cavity 2 through the duct 1 I so as toproduce an atmosphere at a pre-determined pressure therein. When a highfrequency current through the induction winding 4, the electromagneticfield it induces inside the cavity forms a plasma thereon. The dischargewhich takes place in the plasma causes a great increase in thetemperature of the inside wall of the cavity, this producing adistilling of the inner wall and the establishing of a vapor pressure ofthe substance to be deposited. This distilled substance escapes throughthe opening 3 and is deposited on the substrate 7. In the arrangementaccording to the invention, the plasma is confined inside the cavity.

It has been noted that the thin layers thus obtained consist of crystalswhich are appreciably larger and better formed than those obtained byreactive projection. It has also been noted that the crystallinedirection of the thin layers is perfect.

In this device according to the invention, the walls of the cavityconstitute a thermal screen. In certain embodiments, the latter havebeen reinforced by arranging a second cavity round the first. Thisscreen effect enables the energy dissipated in the plasma to be increased so as to bring the inside surface of the cavity to a very hightemperature in the order of several thousands of degrees without dangerfor the insulating tube 1.

In the particular embodiment shown in FIG. 1, the device comprises,moreover, an electrode 12 in the opening 3 formed in the cavity 2. Thiselectrode 12 is connected to an appropriate electrical potential supplyV so as to produce a spark suitable for promoting the starting up of theplasma.

In a varied version of an embodiment, the tube 1 is surrounded by acooling funnel. It is thus possible to obtain high evaporating speedsand relatively high vapor pressures inside the cavity, this promotingmolecular combination.

In a particular example of an embodiment, a cylindrical cavityconsisting of zinc oxide, 50 mm in diameter and 60 mm in height, hasbeen placed in a quartz tube. An induction winding consisting of threeturns made of copper tubing 6 mm in diameter, connected to ahighfrequency power generator, has been arranged about the tube, on thelevel of the cavity.

After having produced a vacuum in the order of 10 mm Hg in the tube 1,and after having heated the substrate to a temperature of 200C, oxygenhas been injected in the cavity in order to produce a pressure in theorder of 5.10' mm Hg therein. The pressure in the container in which thesubstrate is placed is appreciably lower subsequent to the loss of headat the outlet of the cavity.

After having started up the high-frequency generator so that it suppliesa power of 4 kw at 3 mc/s, the rated power is reached after barely a fewminutes, and the zinc oxide is then deposited on the substrate in theform of a thin layer which has reached a thickness of 0.5 micron in oneminute.

According to another form of the invention, the induction meansimplemented to generate the plasma inside the cavity is placed in thevacuum about the cavity. Various precautions are taken in that case toavoid the pollution of the substrate. This embodiment, shown in FIG. 3,comprises a cylindrical cavity placed in a vacuum container shown in thefigure only by its base 30. This cavity 20 is lined inside with thematerial 21 to be sprayed, it comprises, at its upper part, a centralopening 22, and at its lower part, a gas inlet 23. The lateral face 24of that cylindrical cavity 20 is surrounded by the turns 25 of aninduction circuit 26, fed by a HF supply, not shown, arranged outsidethe container. This induction circuit 26 consists of a hollow conductorinternally cooled by a water circuit 27, 27 The induction circuit isheld in position by an insulating base 28 fixed to the base 30 of thecontainer. The conductor forming the induction circuit is itself linedwith a layer of protective insulating material 29, made of teflon, in aseries of experiments, and of glass in another series of measurements. Aprotective screen 31 made of insulating material completes theprotection of the substrate with respect to any pollution caused by themetal forming the induction circuit. A seal ring 32 made of refractorymaterial which is a bad heat conductor arranged round the opening 22 ofthe cavity 20 provides a poor heat contact between the cavity 20 and theinsulating screen 31 while providing satisfactory sealing.

The embodiments described obviously have no limiting character, and,needless to say, varied versions may easily be conceived by the man inthe art. The excitation of the plasma in the cavity has, for example,also been obtained by means of a wave guide device. The cavity has alsobeen divided into fragments in certain cases, so as to enable apenetration of the electromagnetic field in the case of very conductiveor refractory substances.

The applicant has also produced a device in which the cavity is drilledwith several openings so that several substrates are coveredsimultaneously.

Moreover, the cavity has been divided into several compartments withoutan appreciable reduction in the depositing speed having been noticed.

It must be understood that the devices according to the invention may beused to great advantage, for producing thin layers of varioussubstances: piezo-electric, semi-conductive, optical, magnetic,insulating substances, materials having great dielectric constancy,refractory materials or compounds thereof having a high metling point.

What is claimed is:

l. A plasma deposition device comprising:

a vacuum container formed of an insulating material,

means for maintaining said container at high vacuum,

a substrate support within said container,

a substrate carried thereby,

means defining a cavity lined on its inside with the substance to bedeposited and having an opening therein adjacent to the substrate, thewall of said cavity being formed of an insulating material, ahigh-frequency excitation means for generating an electromagnetic fieldwithin said cavity, and

means for injecting into said cavity a gas at a predetermined pressurefor promoting the formation of a plasma in the cavity in the presence ofthe electromagnetic field.

2. The device according to claim 1, wherein: said cavity is of generallycylindrical shape and defined by the cylindrical wall provided on itsinside with longitudinal ribs.

3. The device according to claim 1, further comprising: an electrode inthe cavity; said electrode being connected to an electrical potentialsupply producing a spark to promote the starting up of the plasma.

4. The device according to claim 2, wherein: said high-frequencyexcitation means comprises an induction winding surrounding theinsulating container at the level of the cavity and means connectingsaid induction tion winding within the vacuum container and surwindingto a high-frequency voltage supply. rounding said cavity which is linedon its inside with the 5. The device according to claim 3 wherein: saidsubstance to be deposited. high-frequency excitation means comprises aninduc-

1. A plasma deposition device comprising: a vacuum container formed ofan insulating material, means for maintaining said container at highvacuum, a substrate support within said container, a substrate carriedthereby, means defining a cavity lined on its inside with the substanceto be deposited and having an opening therein adjacent to the substrate,the wall of said cavity being formed of an insulating material, ahigh-frequency excitation means for generating an electromagnetic fieldwithin said cavity, and means for injecting into said cavity a gas at apre-determined pressure for promoting the formation of a plasma in thecavity in the presence of the electromagnetic field.
 2. The deviceaccording to claim 1, wherein: said cavity is of generally cylindricalshape and defined by the cylindrical wall provided on its inside withlongitudinal ribs.
 3. The device according to claim 1, furthercomprising: an electrode in the cavity; said electrode being connectedto an electrical potential supply producing a spark to promote thestarting up of the plasma.
 4. The device according to claim 2, wherein:said high-frequency excitation means comprises an induction windingsurrounding the insulating container at the level of the cavity andmeans connecting said induction winding to a high-frequency voltagesupply.
 5. The device according to claim 3 wherein: said high-frequencyexcitation means comprises an induction winding within the vacuumcontainer and surrounding said cavity which is lined on its inside withthe substance to be deposited.